Field of the Invention
The present invention relates to a vehicle body frame structure of a motorcycle.
Description of the Related Art
As a vehicle body frame structure of a motorcycle, for example, Patent Document 1 discloses one provided with a front frame formed of a head pipe and a pair of right and left tank rails, and a rear frame formed of rear-arm brackets and upper and lower cross members. The rear frame is formed in a manner that the pair of right and left rear-arm brackets, the upper cross member connecting mutual upper end portions of these rear-arm brackets, and the lower cross member connecting mutual lower end portions of the rear-arm brackets are integrally formed. The rear-arm brackets are formed to exhibit a quadrangular shape in a cross section having a hollow portion, with the use of an outer plate on the outside of the vehicle body, an inner plate on the inside of the vehicle body, a front wall and a rear wall connecting these both side plates, and the like. Further, at a center part in an up-and-down direction of the rear-arm brackets, there are formed shaft holes each for pivotally supporting a rear arm supporting pivot shaft, by thickening the front wall.
[Patent Document 1] Japanese Laid-open Patent Publication No. 2004-114719
However, in the vehicle body frame structure of the motorcycle disclosed in Patent Document 1, the pivot shaft is provided so as to be adjacent to the hollow portion of the rear-arm bracket (refer to FIG. 14 in Patent Document 1). Although it is ideal that a periphery of the pivot shaft has a high rigidity for a driving stability, if the pivot shaft is provided so as to be adjacent to the hollow portion, it is difficult to provide a high rigidity to the periphery of the pivot shaft.